Seizure Types

What is a seizure?

A seizure is a sudden burst of electrical activity in the brain, which causes a disturbance in the way brain cells communicate with each other. The kind of seizure a person has depends on which part and how much of the brain is affected by the electrical disturbance that produces seizures.

Different parts of the brain are specialized to do different things. There are parts of the brain that help us speak, understand those around us, and coordinate our movements. Our brains are involved in everything we experience, think, say, feel or do. Any one of these functions can be altered or disrupted during a seizure.. A seizure may take many different forms including a blank stare, uncontrolled movements, altered awareness, odd sensations, or convulsions.

Seizures are usually brief and can last anywhere from a few seconds to a few minutes. The brain is very good at stopping seizure activity. Immediately afterwards, a person may have no lingering effects or they could experience temporary residual effects, such as muscle weakness or confusion, which resolve.

People with epilepsy may experience more than one type of seizure.

Seizure Categories

Seizures are divided into two main categories: focal and generalized. The category is determined by the location of the seizure activity within the brain at the beginning of the seizure.

Focal Seizures

Previously called partial seizures.

Focal seizures start in a particular site, or ‘focus’, within one brain hemisphere.

The location of the seizure activity in the brain will determine what the seizure will look or feel like. A focal seizure in the part of the brain responsible for hearing could cause a sudden but temporary distortion in sound or the person could hear a sound that isn’t there (i.e. an auditory hallucination). A focal seizure in the part of the brain responsible for controlling finger movements could cause a sudden twitching of one or more fingers on the opposite side of the body.

Focal seizures can vary a lot from one person to another because of the wide range of functions that our brains control. However, an individual with a single seizure focus may have the same experience each time their seizure starts.

Previously called simple partial seizures.

During this type of seizure a person will be fully alert, aware of everything that is happening, and able to have a conversation with others. People often refer to this seizure as an aura if they experience things that are not visible to others such as an unusual feeling. Focal seizures with retained awareness could also result in visible changes, for example twitching of certain muscles on one side of the body or an uncontrollable movement.

Previously called psychomotor seizures or complex partial seizures.

This type of focal seizure causes a change in awareness or in thinking abilities. The name has changed to focal dyscognitive seizures because this focal seizure is associated with a temporary disruption (Greek prefix “dys“) in thinking abilities, or cognition. During a dyscognitive seizure a person may have trouble communicating or understanding language. They might have a blank stare and could be unresponsive. Some people exhibit repetitive movements or automatic behaviours, such as chewing movements, rearranging objects or fiddling with clothing. Healthcare providers call these behaviours “automatisms”. Some people wander during a dyscognitive seizure.

Some individuals who exhibit unusual behaviours during a dyscognitive seizure could be mistaken for being under the influence of alcohol or drugs. People could also be mistakenly viewed as uncooperative if they do not respond to someone’s questions or instructions during a dyscognitive seizure.

The seizure activity may remain in the part of the brain where it begins or it may spread to other areas in the brain. Some focal seizures evolve to a bilateral (both the left and right hemispheres) convulsive seizure.

When a focal seizure with altered awareness ends, the person may initially be confused and disoriented. This can make it difficult to tell exactly when the seizure (or ictal period) has ended and the post-ictal phase that follows the seizure has begun.

Generalized Seizures

Generalized seizures quickly spread across the left and right hemispheres of the brain. Some people experience an aura at the beginning of a generalized seizure. Many, but not all, generalized seizures are associated with a loss of consciousness.

Generalized seizure activity occurs in the bumpy outer layer of the brain, known as the cortex, but does not always involve the entire cortex. There may also be seizure activity in some of the deeper brain structures underneath the cortex.

Most generalized seizures cause changes in the body’s muscles, such as a stiffening of the muscles (tonic), a decrease in muscle tone (atonic), rhythmic jerking movements (clonic), or a sudden twitch or jolt-like movement (myoclonic). These various types of muscular changes are associated with different types of generalized seizures, as listed below, but could occur during focal seizures too. The description of what happens during the seizure, along with any changes that happen before or after the seizure, are important features used by a healthcare provider to determine the seizure category and the seizure type. The duration of the seizure is another important feature.

For most people, this is the type of seizure they think of when they think of epilepsy. During the seizure there are two phases, tonic (a stiffening of the muscles) and clonic (rhythmic jerking of the muscles). These phases can happen in any order, but most often the tonic phase is first, followed by the clonic phase.

Tonic Clonic seizures can occur if someone has primary generalized epilepsy and the seizure is generalized seizure from the very start. A tonic-clonic seizure can also occur if someone has focal epilepsy if their focal seizure evolves to become a bilateral convulsive seizure. Tonic-clonic seizures can also occur when people do not have epilepsy and can be brought on (or provoked) by various things such as fever, infection, low blood sugar or alcohol withdrawal.

The typical length of a Tonic Clonic seizure is from under a minute to a few minutes. Like other seizures, these seizures generally run their course and end naturally on their own. When the person regains consciousness they will usually be confused and will gradually reorient themselves to where they are and what has happened. People are often tired after a Tonic Clonic seizure and may want to rest.

These seizures are very brief, about 9 seconds on average. The most striking feature is a blank or vacant look that could be misinterpreted as a brief episode of daydreaming. The blank look may be the only outward sign, although some people have other features that could include eye movements, blinking or automatic behaviours. An absence seizure would typically start abruptly and end abruptly. After the brief seizure, the person will generally carry on with whatever they had been doing before. These seizures can go unnoticed or if noticed they may not be recognized as being a seizure.

These seizures cause rhythmic jerking movements. When the rhythmic jerking movements are the only feature, it is a clonic seizure. These types of movements occur more frequently in association with a phase of muscle stiffening (see tonic-clonic seizures above).

These seizures cause the muscles to stiffen. If a person is standing, a sudden increase in muscle tone could cause them to fall. Some people call this a “drop attack”. Generalized tonic seizures could also cause a sudden stiffening (or contraction) of the muscles in both arms. These seizures usually last less than 20 seconds, but sometimes they could be up to about 60 seconds.

These seizures cause a loss of muscle tone which means the individual suddenly becomes limp. If a person is standing, the sudden loss of muscle tone will cause them to fall. Therefore, both tonic seizures and atonic seizures can be associated with episodes that people may refer to as drop attacks.

These seizures are extremely brief, jolt-like movements that resemble a startle response. They are usually less than a second in length. For example, an individual could have a sudden jerk of their upper arms or shoulders. Sometimes the muscle contractions are subtle and may not be visible to an observer.